Bioresorbable stent

ABSTRACT

A stent having a tubular framework structure consisting of interconnected stent struts, fabricated as a whole from a bioresorbable material and being convertible from a compressed first geometric shape into a radially dilated, dimensionally stable, tubular second geometric shape. 
     Characterized by all of the stent struts of the tubular framework structure has made of a uniform bioresorbable material, the tubular framework structure comprises at least one surface region, which is congruent in one piece and is situated on a lateral cylindrical surface the surface, region comprising stent struts surrounded by stent struts of the framework structure that are adjacent to the surface region, such that the stent struts within the surface region have a smaller amount by weight of bioresorbable material per one predefinable discrete strut length, than the stent struts of the framework structure adjacent to the surface regions.

CROSS-REFERENCE TO RELATED APPLICATIONS German Patent

Application 10 2013 004 625.4, filed Mar. 16, 2013, the completedisclosures of which are hereby incorporated herein by reference intheir entirety for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a stent with a tubular framework structurehaving interconnected stent struts, the entire framework structure beingmade of a bioresorbable material and being convertible from a compressedfirst geometric shape into a radially dilated, dimensionally stabletubular second geometric shape.

DESCRIPTION OF THE PRIOR ART

In vascular medicine, stents refer to medical implants for mechanicaldilatation and support of hollow organs, in particular arterial bloodvessels. For the purposes of the most gentle possible implantation,preferably by means of catheter support, minimally invasive surgicaltechniques, stents are typically made of a plastically deformableframework structure in tubular form, usually produced from metal or ametal alloy, the diameter of the tube being expandable from a smallfirst diameter, at which it is possible to insert the stent withoutharming the patient and to position the stent inside the body, to asecond larger tube diameter, at which the stent manifests itstherapeutic effect for vascular support and radial vascular dilatation,in particular on stenosed sections of the vascular wall.

In addition to the desired therapeutic stent effect, adverse effects mayalso occur with the intracorporeal implantation of stents, which isusually permanent. These adverse effects originate from endogenousdefensive reactions to the stent as a foreign body. Tissue irritation isunavoidable due to the force-activated mechanical contact between theradially dilated tubular framework structure of the stent and thevascular wall. Depending on the extent of this tissue irritation, it maycause inflammatory reactions, which can lead to the development ofthromboses or restenoses. To counteract such medical complications,stents having biocompatible polymers or ceramics impregnated withmedications, with coatings and/or with openings in the form of pores,are known, so that medications can be released into the vascular wall bydiffusion. The publication WO 2012/057976 describes a stent havingopenings in the stent struts, comprising a polymer that contains amedication.

Due to the permanent implantation of stents, there is thus an increasedrisk of thrombi, for the restriction of which it is at least recommendedthat concomitant antithrombotic medication be administered permanently.

Although the framework structure of a stent is permeable for solids andfluids due to its open-mesh framework structure, stents that are to beimplanted in vascular regions, where there is a vascular branch coveredby a portion of the open-mesh framework structure, neverthelessconstitute significant obstacles to flow. To eliminate this problem,special stents have been developed for use in the main branches and sidebranches of human blood vessels. The publication US 2012/0209368 A1describes a stent system and a method for implantation of same, in whichthe vascular side branch branching off from a main vascular branch isdilated by a separate stent to form a stent, which is situated along themain branch in the region of the outgoing side branch. However, thedisadvantage of this special side branch stent system is that thelarge-volume implant leads to a substantial foreign body reaction andthus often results in relapse stenoses in the treated vascular region.

Alternative stent designs with large holes or recesses, so-called“open-cell designs” or “fenestrations,” which are implemented in a stentdescribed in the publication EP 2 497 444 A1, to create better accessfrom a main vascular branch to corresponding side branches, have thedisadvantage that vascular constrictions are constantly occurring due totissue protrusions precisely at the locations where the stent body has alarge hole or a fenestration.

The disadvantages associated with permanent stent implantation can bereduced with a new generic type of stent that has been known and in usefor quite a while. These stents have stent struts made of bioresorbable,bioabsorbable or biocorrodible materials, which are capable ofdissolving completely inside the body and therefore at least limit theperiod of time of physical stresses caused by the stent.

The publication WO 2009/155206 A2 discloses one such bioabsorbable stentmade of a bioresorbable polyester, which is degraded successively in thebody and/or dissolves completely over a period of time. A stent made ofa magnesium alloy is described in the publication WO 2008/118607 A2,This stent also has properties of degradation by means of bioresorptionor biocorrosion.

Use of dissolving bioresorbable stents leads first to an improvement inthe biocompatibility problems that have occurred with the nondegradablestent materials known in the past as well as to a time restriction ondefensive physical reactions that cause the development of thromboses.Furthermore, it is no longer necessary to remove implanted stents by asurgical procedure, even if the procedure is only minimally invasive.

Nevertheless, the use of such stents is incapable of solving theproblems associated with implantation inside a hollow organ in theregion of at least one vascular branch, especially since a stentimplanted in an arterial main vessel in the region of vascular branchesor vascular outlets will also in this case displace the vascular outletsdue to the stent struts and will thus have a permanent influence on theflow dynamics in this vascular region.

WO 2009/009376 A2 describes a stent having a bioresorbable membrane. Thestent has a tubular framework structure comprised of a plurality ofstent struts designed in the form of a meandering ring, connected to oneanother by connecting struts. The resulting framework structure of thestent encloses a surface region on the lateral surface that can beassigned to the stent, within which the framework structure deviatesfrom the remaining framework structure of the stent. Thus, the stentstruts situated inside the surface region are arranged and designed insuch a way that they can be dilated to form a side stent structureoriented laterally to the stent and forming collars or also formingtubes. Nevertheless, the stent struts are surrounded by an additionalbioresorbable membrane, both inside and outside the surface region, thestent ultimately implanted constitutes a permanent intracorporealforeign body that causes irritation to the respective vascular area.

The publication WO 2009/009311 A2 describes a similar stentconfiguration, which has a tubular framework structure, which likewise,as in the present case, has a surface region bordered by acircumferential edge, within which a modified framework structure isprovided to form a side stent structure that serves to support avascular branch for the purpose of implantation in a vascular areahaving a vascular branch. Based on the finding that a stent structuredesigned for the purposes of implantation inside a vascular branchingregion experiences an increased mechanical stress to support the mainvessel and the branching secondary stent to support the vascular branch,that is in the region of the circumferential edge mentioned above, theknown stent configuration provides stent strut parts made ofbioresorbable material in the region of the circumferential edge.Mechanical stress moments in the region of the transition between themain branch and the secondary branch of the stent configuration can beprevented by such stent strut components that dissolve automatically inthe body. Likewise, the disadvantages associated with the stent sectionslocated permanently in the respective vascular regions persist, asexplained above.

The stents, which are disclosed in the publication DE 10 2010 027 124A1, which are made of a biodegradable magnesium alloy, advantageouslyoffer the possibility of being dissolved completely intracorporeally.Stents that dissolve completely intracorporeally have differentdissolving properties because of their different absorption propertiesdue to variations in the alloy composition (grain fineness) of the stentstruts. The corrosion rate can thus be influenced in such a way that animplantation region dissolves more rapidly in the area of a bifurcationthat is a vascular branch, than another implant region, so that the flowthrough the side vessel is ensured.

U.S. Pat. No. 8,109,991 B2 describes a stent that is not completelyresorbable but instead has only bioresorbable connecting elementsbetween individual annular stent elements. The connecting elementsshould dissolve to permit an improved adaptation of the stent tomovements of the vessel and thus a reduction in complications.

US Published Patent Application Publication 2003/0 199 993 A1 describesa bioresorbable implant that has different dissolving rates over time.The implant therefore has a layered structure comprised of differentmaterials and particles may be introduced additionally into theindividual layers. Different absorption rates can be adjusted locally inthe implant due to local variations in the distribution of theparticles.

US Patent Application Publication No. 2012/0150275 A1 discloses abioresorbable stent that is created by printing an “ink-like” materialon a carrier body. The special advantage of this method is that aseamless stent can be produced.

DE 10 2005 018 356 A1 relates to resorbable implants made of aresorbable base body and a biodegradable coating. The base body is ametal, a metal alloy, a metal salt, a polymer or mixtures of thesecompounds. However, the biodegradable coating preferably hasbiodegradable polymers and also contains at least one pharmacologicallyactive substance.

SUMMARY OF THE INVENTION

The invention is based on improving a stent for implantation in anintracorporeal vascular region having at least one vascular branch, suchthat it is ensured, firstly, that the at least one branching vascularchannel is not covered by the implanted stent to thereby prevent anegative influence on the flow conditions, in particular in the regionof the vascular branch. Secondly, care should be taken to ensure thatthe implanted stent causes little or no tissue irritation due to itsforeign body properties, so that the risk of inflammation-inducedthromboses can be ruled out or at least reduced significantly on along-term basis. Associated with this, the goal is to create theprerequisites for making the antithrombotic medication, which has so farbeen required for treatment of patients, superfluous. Another aspect isto ensure that it is possible to prevent stent fragments that have notdissolved completely in the process of decomposition of the stent frombecoming detached from the remaining stent framework and entering thebloodstream as dangerous foreign bodies. Finally, it should be possibleto manufacture the stent as simply and thus inexpensively as possible.

The invention is directed to a stent having a tubular frameworkstructure having interconnected stent struts manufactured as a wholefrom a bioresorbable material and is convertible from a compressed firstgeometric shape to a radially dilated, dimensionally stable, tubularsecond geometric shape. With the framework structure made completely ofbioresorbable material, this creates the prerequisite for being able toprevent ongoing irritation of the tissue regions in contact with thestent, which is associated with the implantation of a stent. This is thecase in particular because the therapeutically effective lifetime ofsuch a stent is limited. Through a suitable choice of materials to formthe stent and/or providing a coating that delays bioresorption on thesuitably selected stent material, the therapeutic lifetime of the stentcan be defined almost precisely on the order of magnitude of yearsand/or months. The modification of such a stent made entirely ofessentially known bioresorbable material conditions the stent struts ona lateral surface that can be attributed to the tubular frameworkstructure of the stent within at least a certain surface region that iscohesive in one piece, that is enclosed by an essentially closedcircumferential edge, such that these stent struts are capable ofdissolving by bioresorption in a shorter period of time afterimplantation in a hollow organ in a patient than the stent strutsoutside of the at least one certain surface region. In this way, alateral opening is formed within the tubular framework structure afterthe stent struts situated inside the surface region have completelydissolved. This opening is adapted in size and shape to the vascularbranching within the hollow organ in which the stent has been implantedin a suitable way.

In the design and conditioning of the stent struts situated inside thecircumferential edge, attention must be paid to the fact that no stentstrut constituents that have not yet been completely bioresorbed becomedetached from the surrounding stent struts situated inside the surfaceregion and thereby entering the bloodstream as foreign bodies regardingtheir complete dissolution by way of bioresorption. To rule out suchseparation phenomena, measures must be taken with the invention, so thatstent struts within the surface region at the greatest distance from thecircumferential edge are capable of dissolving within a shorter periodof time than the stent struts that are close or directly adjacent to thecircumferential edge.

According to this invention, the amount by weight of bioresorbablematerial per strut length of the stent struts decreases continuously orgradually within the surface region, that is in increments, with anincrease in the distance of the stent struts from the circumferentialedge. Thus for example the stent struts situated centrally within thesurface region have smaller stent diameters than the stent struts insidethe surface region, which are arranged near the circumferential edge orare directly adjacent thereto.

Alternatively or in combination with the preceding measure, it isrecommended that the different dissolving power of the stent strutswithin the surface region over time be accomplished by a suitablevariation in the layer thickness of a bioresorbable material layerdeposited on the stent struts inside the surface region. If, forexample, the bioresorbable stent formed according to the invention iscoated with a first material layer, which preferably has a uniform layerthickness on the coated regions of the framework structure and thiscoating is applied to the stent struts of the framework structure to theexclusion of the stent struts inside the surface region, then depositionof a second material layer on the stent struts inside the surface regionmakes possible the different dissolving powers of the stent strutsinside the surface region, as mentioned above, due to suitablevariations in layer thickness. The layer thickness of the at least onesecond material layer is reduced continuously or gradually with anincrease in the distance from the circumferential edge. This ensuresthat the stent struts inside the surface region will dissolve completelyand the most rapidly by bioresorption are those the farthest away fromthe circumferential edge enclosing the surface region.

This novel stent is thus capable of, on the one hand, radially dilatingthe stenosed hollow organ after dissolving the respective stent strutsthat initially cover the vascular branch, and then, on the other hand,ensuring free lateral access to a secondary vessel branching off fromthe hollow organ.

Since the stent according to the invention differs only insignificantlyor not at all from the known stents in the starting state, that is inthe state prior to and during the process of implantation, so that thestent is handled in the same way using minimally invasive surgicaltechniques. The process of radial dilatation by a balloon catheter, forexample, after corresponding intracorporeal positioning of the stentdoes not differ from the dilatation of known stents. In intracorporealpositioning of the stent, the surgeon needs to only additionally takeinto account the fact that the stent lies axially and in its peripheraldirection exactly opposite a lateral opening region of a vascularbranch. The stent therefore has radiopaque markers that are attachedsuitably to the stent for marking the surface region, enabling thesurgeon to position the stent accurately.

Since the complete framework structure of the stent dilating the holloworgan is manufactured of a bioresorbable material, the stent dissolvesautomatically and, along with it, the associated supporting function, sothat the disadvantages associated with permanent retention of a stentinside a vessel are avoided. The maximum dwell time of the stent made ofbioabsorbable material can be defined through a suitable choice ofmaterial, shape and size for the design of the stent struts making upthe framework structure.

To ensure that, after implantation, the stent struts situated inside theat least one surface region, as explained above, are subject to a morerapid dissolution by way of bioresorption than the remaining frameworkstructure, the following measures are recommended as alternatives or tobe used in combination:

A first possibility for rapid dissolution of the stent struts providedinside the surface region is by designing these stent struts with asmaller amount of the weight of bioresorbable material per predefineddiscrete strut length than the stent struts of the remaining frameworkstructure directly or indirectly adjacent to the surface region.

Since the bioresorption rate, that is the dissolving power over time, ispredefined by the bioresorbable material itself, the implanted stentdissolves at a uniformly rapid rate over its entire spatial extent. Dueto the smaller amount by weight per length of strut pertaining to thestent struts provided inside the surface region, these are capable ofdissolving in a shorter amount of time than the stent struts in theremaining framework structure region. One possible measure for reducingthe amount by weight per strut length pertaining to the stent strutssituated inside the surface region is to reduce the stent strut diameterin comparison with the stent struts situated outside of the surfaceregion. It is also sinsable to design the stent struts to be hollowwithin the at least one surface region in comparison with a solid stentstrut design in the remaining framework structure region of the stent.The latter measure makes it possible to design stent struts with auniform stent strut diameter throughout the entire framework structureof the stent, so that a uniform structural stability can be implementedover the entire stent.

Another alternative measure for completely dissolving the stent strutssituated inside the at least one surface region in a shorter period oftime is to coat the framework structure having uniform bioresorbablematerial with an additional layer of material that delays thebioresorbability of the framework structure, except for the stentstructures situated inside of the at least one surface region.Furthermore, the coating of the framework structure is not a complex andexpensive measure in terms of the process technology, except for thosestent struts situated inside the at least one predefined surface regionwith a material layer having a bioresorbability-reducing effect.

It is of course possible to combine the two measures described above, sothat a stent having stent struts situated inside the at least onesurface region that have a smaller amount by weight per length of strutin comparison with the remaining stent region is additionally coatedwith a material layer having a material having abioresorbability-reducing effect, wherein the stent struts that areinside the at least one surface region are excluded from the materialcoating. A stent conditioned in this way has a longer lifetime incomparison with the stent struts that are situated inside the surfaceregion and are therefore uncoated and are also designed to be thin, sothat they are capable of dissolving completely after a suitably shortimplantation time and thus leading to a lateral opening inside theframework structure of the stent, which in this form ensures free andunhindered access to a vascular branch, while the vascular tissuedirectly surrounding the vascular branch remains inside the holloworgan, supported by the framework structure of the stent and/or dilatedradially.

A third alternative for individual fabrication of the bioresorptionbehavior of the stent structures situated inside the at least onesurface region in comparison with the stent struts of the remainingframework structure of the stent is to coat the stent struts, except forthe stent struts situated inside the at least one predefined surfaceregion, using at least one first bioresorbable material layer. The stentstruts situated inside the at least one surface region are coated withat least one second bioresorbable material layer, which is completelybioresorbable in a shorter period of time than the first bioresorbablematerial layer.

The third alternative is to combine with the measure mentioned first, isto the stent struts situated inside the at least one surface region havea smaller amount by weight of bioresorbable material per strut length incomparison with the stent struts in the remaining stent region and arealso coated with the aforementioned material layer containing the atleast one second bioresorbable material layer.

The at least one second bioresorbable material layer does not need tonecessarily be a bioresorbable material that is different from the firstbioresorbable material layer. Instead, it is possible to produce thefirst and second material layers from identical bioresorbable material,but in this case, the layer thickness of the bioresorbable materiallayer within the at least one surface region is to be selected to besmaller than the material layer of the first bioresorbable materiallayer in the remaining stent region. This ensures that the secondmaterial layer, which is designed to be thinner, will dissolvecompletely due to bioresorption after a suitable implantation timewithin a shorter period of time than the first bioresorbable materiallayer, which is designed to be thicker.

Implementations of the stent designed according to the invention are ofcourse also possible, in which the at least one first layer of materialand one second layer of material differ from one another in the type ofmaterial.

A preferred embodiment of the stent has a tubular framework structure,which has a uniform framework structure, that is the stent struts have auniform mesh pattern or arrangement pattern and enclose open frameworkstructure meshes having a geometric repeating period with these meshespreferably having a uniform mesh size. For economic reasons as well asfor reasons of access to known and proven manufacturing techniques, allstent struts forming the framework structure are produced from a uniformbioabsorbable material and can be joined together in one piece,depending on the type of fabrication, or joined and/or woven together inthe form of a braid to form a braided framework structure.

The size and shape of the tubular stents are to be selected inaccordance with the size and shape of the hollow organ to be treated.This is also true in particular for the number of surface regions to beprovided along the lateral surface of the tubular stent as well as theirsize and shape, which are to be selected accordingly based on thedifferent vascular branches leading away from the hollow organ at theside. Thus, depending on the size and shape of the vascular branch, thecircumferential edge enclosing the at least one surface region may becircular, elliptical or oval or may have an n-angular shape, where n isa natural number ≧3. The circumferential edge may be embodied as avirtual bordering line that is a line that is not physically manifested.This is the case when the framework structure has a homogeneouslypermeable mesh structure, wherein the stent struts are designed in onepiece and are continuous in the transition to the at least one surfaceregion. Likewise, the surface region may be surrounded by acircumferential edge in the form of a closed stent structure, which,however, is designed in such a way that it permits radial dilatation ofthe stent.

It is of course also possible to combine the preceding measures withrespect to the deposition of the material layer(s) with the variousembodiments of amount by weight per strut length of the stent struts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below as an example without restrictionof the invention on the basis of exemplary embodiments with reference tothe drawings, in which:

FIGS. 1 a, b and c show schematic diagrams of a stent designed accordingto the invention; and

FIGS. 2 a, b and c show schematic diagrams of possible embodiments toform stent struts inside the at least one surface region.

DESCRIPTION OF THE INVENTION

FIG. 1 a shows a highly schematic diagram of a tubular stent 1, whichhas a stent diameter d which has not been dilated radially. FIG. 1 bshows the same stent in a radially dilated form with a stent diameterD>d. The stent 1 has a framework structure 3 made of stent struts 2 (seeFIG. 1 b), which, as a whole, are a bioresorbable material. Theindividual stent struts 2 making up the framework structure are looselyor tightly connected to one another at connection points 4 and eachencloses framework meshes 5 designed to be open. The individual stentstruts 2 making up the framework structure 3 preferably are consist of abioresorbable metal or a bioresorbable metal alloy, wherein the metal isone of the metals listed below, or the metal alloy contains at least onemetal from the following metals: magnesium, zinc, zirconium, carbon,iron, sodium, calcium, manganese, molybdenum or selenium. It is alsopossible to fabricate the stent struts 2 from a bioresorbable polymer ofthe family of poly-(L-lactides), poly-lactide-co-glycolides orpoly-glycolactides, poly-carbonates, polychitosans or phospholipids.Through the choice of material as well as the material thickness ofwhich the individual stent struts are fabricated, the dissolvingproperties can be determined in advance by way of bioresorption of thestent after implantation inside the body. It is thus possible inparticular to define and stipulate the therapeutic duration of effect ofthe implanted stent in advance, that is to stipulate in advance thenumber of years and/or months, after which the stent 1 will lose itstherapeutic effect of dilating the hollow organ after implantation andthen dissolve completely ultimately by way of bioresorption.

In contrast with known stents, which dissolve completely by way ofbioresorption, the stent designed according to the invention has asurface region 6 which is situated on the lateral surface M of thegeometric shape of the stent 1, which is designed in the form of a tubeor a hollow cylinder. This surface region is surrounded by a virtual orreal circumferential edge 7 and separates the surface regions 6 from thestent struts of the remaining framework structure of the stent 1. In thecase of the exemplary embodiment illustrated in FIGS. 1 a and b, thecircumferential edge 7 is designed to be oval. FIG. 1 b shows the stent1 in a radially dilated state, which is assumed by the stent 1 after theprocess of implantation and radial dilatation. The stent struts 2′situated inside the surface region 6 differ from the stent struts 2situated outside of the surface regions 6 in that they are capable ofdissolving in a shorter period of time after intracorporeal implantationthan the stent struts 2 outside of the surface region 6, namely suchthat the stent struts 2′ are capable of dissolving in a chronologicalorder, from the center out to the circumferential edge 7, within of thesurface region 6.

FIG. 1 c shows the situation after complete dissolution of the stentstruts 2′, which are situated inside the surface region 6. The opening8, which is inscribed by the circumferential edge 7, serves to providefree access to a vascular branch from a hollow organ within which thestent is positioned for dilatation of the hollow organ radially. Theshape and size of the opening 8 are adapted to the shape and width ofthe opening of the vascular branch, so that the flow conditions, whichprevail in the region of the vascular branch, are not impaired.

Radiopaque markers 11 are provided along the circumferential edge 7,enabling the surgeon to position the stent 1 accurately in relation to avascular branch.

Depending on the anatomy of the hollow organs to be treated, indeviation from the exemplary embodiment illustrated in FIG. 1, aplurality of surface regions 6 and/or the resulting free openings 8 maybe provided within a stent 1.

In the schematic detailed diagrams of the surface region 6 inscribed bythe circumferential edge 7 shown in FIGS. 2 a though 2 e are explainedon the basis of the alternative measures, by which dissolution of thestent struts 2′ within the surface region 6 is achieved within a shorterperiod of time in comparison with the amount of time required tocompletely dissolve the framework structure 3 of the stent 1 bybioresorption.

A first embodiment illustrated in FIG. 2 a shows the design of stentstruts 2′ situated inside the surface region 6 and having a smallerstent strut diameter in comparison with the stent strut diameter of thestent struts 2 adjacent to the circumferential edge 7 of the surfaceregion 6 from the outside. Because of the smaller amount 6 by weight onthe outside per stent strut length of the stent struts 2′, which aremanufactured of otherwise the same bioresorbable material as the stentstruts 2 adjacent to the surface area, it is ensured that the stentstruts 2′ will be completely dissolved after an extremely short periodof time, that is within a few weeks or months and will thus result in afree opening 8. The difference due to the difference in the stent strutdiameters with respect to the amount by weight of bioresorbable materialper strut length can amount to at least 1% up to max. 60% between thestent struts 2′ situated inside of the surface region and the stentstruts 2 adjacent to the circumferential edge 7 of the surface region 6from the outside.

An improved embodiment according to the invention in comparison with theexample illustrated in FIG. 2 a is shown in FIG. 2 b. Again in this casethe stent strut diameters of the stent struts 2′ are designed to besmaller in comparison with the stent struts 2 outside of the surfaceregion 6 with the stent strut diameter additionally being variedcontinuously, so that the stent strut diameter of the stent struts 2′decreases with an increase in the distance from the circumferential edge7. The difference due to the difference in the stent strut diameterswith respect to the amount by weight of bioresorbable material per strutlength may amount to at least 1% up to max. 60% between the stent struts2′ situated radially at a distance from the circumferential edge and thestent struts 2′ close to the circumferential edge. This measure ensuresthat the stent struts 2′ situated inside the surface region 6 arecapable of completely dissolving, beginning at their greatest distancefrom the circumferential edge 7, until finally the stent struts 2′ havereached the circumferential edge 7 by dissolving spontaneously by way ofbioresorption and thus form the free opening. It is possible in this wayto rule out partial separation of stent strut portions within thesurface region 6.

Another possibility for time-controlled bioresorption of the stent 1designed according to the invention is illustrated in FIG. 2 c, wherethe stent struts 2 situated outside of the surface region 6 are coatedwith a first material layer 9, whereas the stent struts 2′ situatedinside the surface region 6 are not coated and are designed in the sameway as those in FIG. 2 b. It is obvious that the additional materiallayer 9 results in prolonging bioresorption, so that the uncoated stentstrut portions 2′ are completely absorbed within the surface region 6 ina shorter period of time.

Another embodiment provides for both the stent struts 2 and the stentstruts 2′ situated inside the surface region 6 to be coated with amaterial layer of a uniform material, wherein the stent struts 2′situated inside the surface region 6 are coated with a thinner layer ofmaterial than the stent struts 2 outside of the surface region 6 (seeFIG. 2 d) and the thinner layer of material 9′ also has a continuouslydecreasing material layer thickness, the greater the distance along thestint struts 2′ situated inside the surface region 6 to thecircumferential edge 7. Due to the thinner layer thickness formation ofthe material layer 9′ on the stent struts 2′ inside the surface region6, which should amount to 1% to max. 60% of the material layer thicknessof the material layer 9 outside of the surface region 6, precisely thislayer of material 9′ is dissolved in a shorter period of time than inthe case of the material layer 9 on the stent struts 2 outside of thesurface region 6, so that it is again ensured that the stent struts 2′are resorbed in a shorter period of time than the adjacent stent struts2. The decreasing thickness of the material layer 9′ toward the centerof the surface region 6 also ensures that the stent struts 2′ near thecenter inside the surface region 6 are the first to begin to dissolve sothat the resulting opening within the stent struts 2′ dilates radiallytoward the circumferential edge 7 by way of the continuous resorption ofmaterial. The stent struts 2′ situated inside the surface region 6 taperin an advantageous, although not essential, manner with an increase inthe distance from the circumferential edge 7, as illustrated in theexemplary embodiment according to FIG. 2 b. In this case, however, it isalso conceivable that the effect described here of the dilatationopening from the inside radially to the outside is also established dueto the presence of the second material layer 9′ if the stent struts 2′have a uniform, thin stent strut diameter.

Due to the preferably uniform radial dilatation of the stent strutopening, it is impossible for individual parts to be detached from thestent strut structure network and to enter the bloodstream as foreignbodies and be able to travel around there in an uncontrolled manner. Itis also impossible to additionally apply different layered materials tothe stent struts 2 and_(y) 2′ in addition to the choice of thickness ofthe material layers to be applied to the stent struts 2 and 2′,respectively, wherein care should be taken to ensure that the layermaterial 10 applied to the stent struts 2′ inside of the surface region6 is resorbable more rapidly than the layer material 9 on the stentstruts 2 (see FIG. 2 e). Furthermore, it is also advantageous to designthe at least one second bioresorbable material layer 10 as abioresorbable polymer layer which holds and releases at least onemedication. The at least one medication may preferably be selected fromthe class of antiproliferative substances, the limus group, such assirolimus, everolimus, zotarolimus, the substance class of statins,P2Y12 antagonists or thrombin antagonists.

The alternative design options described above for the purpose of atime-staggered dissolution of the stent struts 2 and 2′ can be combinedin any suitable manner.

LIST OF REFERENCE NUMERALS

-   1 stent-   2 stent struts-   2′ stent struts inside the surface region-   3 framework structure-   4 connecting spot-   5 mesh opening-   6 surface region-   7 circumferential edge-   8 opening-   9 first material layer-   9′ first material layer with a small material layer thickness-   10 second material layer-   11 radiopaque marker

1.-13. (canceled)
 14. A stent with a tubular framework structure ofinterconnected stent struts fabricated from a bioresorbable materialwhich is convertible from a compressed first geometric shape into aradially dilated, dimensionally stable, tubular second geometric shape,comprising: all stent struts of the small tubular framework structurebeing made from a uniform bioresorbable material; the tubular frameworkstructure including at least one surface region, which is congruent inone piece and is situated on a lateral cylindrical surface, the surfaceregion comprising the stent struts that are surrounded by stent strutsof the framework structure that are adjacent to the surface region, suchthat the stent struts within the surface region have a smaller amount byweight of bioresorbable material per discrete strut length, than thestent struts of the framework structure adjacent to the surface regions;the surface region being surrounded by a virtual, self-containedcircumferential edge or an edge that is defined by a stent strutstructure and surrounds the surface region; and an amount by weight ofbioresorbable material per strut length of the stent struts within thesurface region decreasing with an increase in the distance of the stentstruts from the circumferential edge and/or the stent struts of theframework structure adjacent to the surface region are coated with atleast one first bioresorbable material layer, and the stent strutsinside the surface region are coated with at least one secondbioresorbable material layer, which is bioresorbable in a shorter periodof time than the first bioresorbable material layer, and a layerthickness that can be attributed to the at least one second materiallayer decreases continuously or with an increase in distance of thestent struts coated with the second material layer from thecircumferential edge.
 15. The stent according to claim 14, wherein: thetubular framework structure has a uniform framework structure.
 16. Thestent according to claim 14, wherein: the stent struts are connected toone another in one piece and enclose an open framework structure mesh,and all of the framework structure meshes have a uniform shape.
 17. Thestent according to claim 15, wherein: the stent struts are connected toone another in one piece and enclose open framework structure meshes,and all the framework structure meshes have a uniform shape.
 18. A stentaccording to claim 14, wherein: the circumferential edge is circular,elliptical or oval or has an n-angular shape, wherein n≧3 and n is anatural number.
 19. A stent according to claim 15, wherein: thecircumferential edge is circular, elliptical or oval or has an n-angularshape, wherein n≧3 and n is a natural number.
 20. A stent according toclaim 16, wherein: the circumferential edge is circular, elliptical oroval or has an n-angular shape, wherein n≧3 and n is a natural number.21. A stent according to claim 17, wherein: the circumferential edge iscircular, elliptical or oval or has an n-angular shape, wherein n≧3 andn is a natural number.
 22. The stent according to claim 14, wherein:stent struts of the framework structure adjacent to the surface regionare coated with at least one first bioresorbable material layer and thestent struts inside the surface region are uncoated.
 23. The stentaccording to claim 15, wherein: stent struts of the framework structureadjacent to the surface region are coated with at least one firstbioresorbable material layer, and the stent struts inside the surfaceregion are uncoated.
 24. The stent according to claim 16, wherein: stentstruts of the framework structure adjacent to the surface region arecoated with at least one first bioresorbable material layer, and thestent struts inside the surface region are uncoated.
 25. The stentaccording to claim 18, wherein: stent struts of the framework structureadjacent to the surface region are coated with at least one firstbioresorbable material layer and the stent struts inside the surfaceregion are uncoated.
 26. A stent according to claim 14, wherein: thestent struts have smaller stent diameters within the surface region thanthe stent struts of the framework structure adjacent to the surfaceregion.
 27. A stent according to claim 115, wherein the stent strutshave smaller stent diameters within the surface region than the stentstruts of the framework structure adjacent to the surface region.
 28. Astent according to claim 16, wherein the stent struts have smaller stentdiameters within the surface region than the stents struts of theframework structure adjacent to the surface region.
 29. A stentaccording to claim 22, wherein the stent struts have smaller stentdiameters within the surface region than the stent struts of theframework structure adjacent to the surface region.
 30. A stentaccording to claim 14, wherein at least two stent struts inside thesurface region each have an amount of bioabsorbable material per strutlength differing from one another by at least 1% to a max. 60%; and/orat least two stent struts situated inside the surface region are coatedwith second material layer, with layer thicknesses differing from oneanother by at least 1% to a max. 60%.
 31. A stent according to claim 15,wherein at least two stent struts inside the surface region each have anamount of bioabsorbable material per strut length differing from oneanother by at least 1% to a max. 60%; and/or at least two stent strutssituated inside the surface region are coated with second materiallayer, with layer thicknesses differing from one another by at least 1%to a max. 60%.
 32. A stent according to claim 16, wherein at least twostent struts inside the surface region each have an amount ofbioabsorbable material per strut length differing from one another by atleast 1% to a max. 60%; and/or at least two stent struts situated insidethe surface region are coated with second material layer, with layerthicknesses differing from one another by at least 1% to a max. 60%. 33.A stent according to claim 18, wherein: at least two stent struts insidethe surface region each have an amount of bioabsorbable material perstrut length differing from one another by at least 1% to a max. 60%;and/or at least two stent struts situated inside the surface region arecoated with second material layer, with layer thicknesses differing fromone another by at least 1% to a max. 60%.
 34. A stent according to claim22, wherein: at least two stent struts inside the surface region eachhave an amount of bioabsorbable material per strut length differing fromone another by at least 1% to a max. 60%; and/or at least two stentstruts situated inside the surface region are coated with secondmaterial layer, with layer thicknesses differing from one another by atleast 1% to a max. 60%.
 35. A stent according to claim 25, wherein: atleast two stent struts inside the surface region each have an amount ofbioabsorbable material per strut length differing from one another by atleast 1% to a max. 60%; and/or at least two stent struts situated insidethe surface region are coated with second material layer, with layerthicknesses differing from one another by at least 1% to a max. 60%. 36.A stent according to claim 14, wherein: at least one radiopaque markeris applied to the framework structure along a virtual circumferentialedge.
 37. A stent according to claim 15, wherein: at least oneradiopaque marker is applied to the framework structure along a virtualcircumferential edge.
 38. A stent according to claim 16, wherein: atleast one radiopaque marker is applied to the framework structure alonga virtual circumferential edge.
 39. A stent according to claim 18,wherein: at least one radiopaque marker is applied to the frameworkstructure along a virtual circumferential edge.
 40. A stent according toclaim 22, wherein: at least one radiopaque marker is applied to theframework structure along a virtual circumferential edge.
 41. A stentaccording to claim 25, wherein: at least one radiopaque marker isapplied to the framework structure along a virtual circumferential edge.42. A stent according to claim 29, wherein: at least one radiopaquemarker is applied to the framework structure along a virtualcircumferential edge.
 43. The stent according to claim 14, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 44. The stent according to claim 15, wherein the bioresorbablematerial is a metal or a metal alloy and the metal is one of metals or ametal alloy containing at least one element of magnesium, zinc,zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 45. The stent according to claim 16, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 46. The stent according to claim 18, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 47. The stent according to claim 22, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 48. The stent according to claim 25, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy contains at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 49. The stent according to claim 29, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 50. The stent according to claim 35, wherein: thebioresorbable material is a metal or a metal alloy and the metal is oneof metals or a metal alloy containing at least one element of magnesium,zinc, zirconium, carbon, iron, sodium, calcium, manganese, molybdenum orselenium.
 51. A stent according to claim 14, wherein: The bioresorbablematerial comprises one of the bioresorbable polymers of a family of poly(L-lactides), polylactide-co-glycolides or poly-glyco-lactides,polycarbonates, poly-chitosans or phospho-lipids.
 52. A stent accordingto claim 14, wherein: The at least one second bioresorbable materiallayer is a bioresorbable polymer layer which holds and releases at leaseone medication.
 53. The stent according to claim 53, wherein: the atleast one medication is selected from a group of a antiproliferativesubstance class of a limus group comprising at least one of sirolimum,everolimus, zotarolimus, a substance class of statins, P2Y12 antagonistsor thrombin antagonists.
 54. A stent according to any of claim 14,wherein: the at least one second bioabsorbable material layer is a samebioabsorbable material as the first material layer but has a smallerlayer thickness than the first bioabsorbable material layer.